The present invention relates to a data transmission system for use in data transmission and reception in an air conditioning control apparatus and the like.
The data transmission system of the type described generally has a central control unit having a decision and processing function and local devices installed in scattered locations for data transmission and reception between the central control unit and local devices. The central control unit has a data file set up for the local devices so as to call the local devices successively based on the content of the data file for data transmission and reception. Data items collected from the local devices are stored respectively at addresses in the data file which correspond to the local devices. Where there is a need to add or remove a local device or devices, the content of the data file is required to be altered each time such addition or removal is carried out. Therefore, the system is disadvantageous in that its overall arrangement cannot be changed with ease.